1. Field of the Invention
The present invention relates to a screw feed apparatus which is used as e.g. means for driving and feeding a work table disposed in a machine tool and, especially, to a screw feed apparatus of a rolling element circulation type.
2. Description of the Related Art
Conventionally, a ball screw of a tube circulation type, as shown in FIG. 6, comprises a screw shaft “a” having a ball screw groove “b” formed on the outer diameter surface thereof, and a nut “c” having a ball screw groove “d” formed on the inner diameter surface thereof opposed to the outer peripheral surface of the screw shaft; and, between the two ball screw grooves “b” and “d” of the screw shaft “a” and nut “c”, there are interposed a large number of balls “e” in such a manner that they are able to roll. Also, in the ball screw of this type, on the exterior of the nut “c”, there is disposed a return tube “f” which is used to form a return path for the balls “e”. Thus, the balls “e”, which have rolled between the two ball screw grooves “b” and “d” with the rotational movement of the screw shaft “a”, are able to move back to their original positions through the return path formed in the return tube “f”.
According to the ball screw of this type, in the two end portions of the return tube “f”, there are disposed tongue piece portions “g”; and, the balls “e”, which have rolled between the two ball screw grooves “b” and “d”, are made to collide with the tongue piece portions and are scooped up into the return tube “f”. Therefore, due to collision of the balls “e” with the tongue piece portions “g”, not only there are generated noises but also the balls “e” can be damaged.
In view of the above, as shown in FIG. 7, there is proposed and known a ball screw structured in the following manner: that is, in the interior of the nut, there are disposed a plurality of deflector pieces “h” for connecting together a return path formed in the interior of the return tube “f” and a ball rolling path formed between the two ball screw grooves “b” and “d”; and, in each of the deflector pieces “h”, there is formed a ball guide path “i” which can scoop up the balls “e” at an angle substantially coincident with the lead angle of the ball screw grooves “b” and “d” to guide the balls “e” into the return tube “f”.
In the above-mentioned conventional ball screw, since the balls “e” having rolled between the two ball screw grooves “b” and “d” are scooped up at an angle substantially coincident with the lead angle of the ball screw grooves “b”, “d” by the ball guide paths “i” respectively formed in the deflector pieces “h” and are then guided into the return tube “f”, generation of noises and damage of the balls can be prevented. However, because the ball guide paths “i” are complicated in shape and thus formation of the complicated ball guide paths “i” is difficult, there arises a problem that the manufacturing cost of the ball guide paths increases.